1. Technical Field
The present invention relates to a method for producing aldehydes. In particular, the present invention relates to a method for producing aldehydes by subjecting an olefinic compound to a hydroformylation reaction.
2. Background Art
A reaction which comprises reacting an olefinic compound with carbon monoxide and hydrogen in the presence of a catalyst to produce aldehydes or alcohols as their hydrogenated products, is known as hydroformylation reaction. As the catalyst for the hydroformylation reaction, it is common to use an element of Group 8 to 10 of the Periodic Table (hereinafter referred to as a "Group VIII metal"), such as rhodium, modified by a ligand containing phosphorus. It is known that the reaction activity and the selectivity of the product are substantially changed by the ligand used together with the metal component of the catalyst. Accordingly, in order to carry out the hydroformylation reaction industrially advantageously, it is important to improve the reaction activity and the selectivity of the product, and to suppress an olefin-reduced product by a side-reaction. Accordingly, various efforts to design the ligand have been made for this purpose. As such processes, hydroformylation processes employing various phosphine compounds, and hydroformylation processes employing various phosphite compounds, have been reported.
Very few examples have been reported wherein a phosphonite compound is used as the ligand for the hydroformylation reaction. Fewer examples have been reported wherein a phosphonite compound which is not monodentate is used. For example, U.S. Pat. No. 4,400,547 discloses that in a process for a hydroformylation reaction of an olefin employing a non-modified Rh metal as a catalyst, in a step of separating the catalyst, PhP(OPh).sub.2 or EtP(OPh).sub.2 is added as an organic phosphorus compound to stabilize rhodium. However, the ligand in the phosphonite compound is removed after the step of separating the catalyst, and it is not shown that the phosphonite ligand is effective for the oxo reaction system. Further, He Binglin et al. have reported an example wherein a hydroformylation reaction of diisobutylene is carried out by using an Rh catalyst and a phosphonite compound bonded to a polymer having many functional groups introduced thereto or to a styrene-divinylbenzene copolymer (&lt;polymer&gt;-P(OEt).sub.2). This document describes that results of a degree of conversion of 64.3%, an yield of aldehyde of 60.8% and an yield of alcohol of 3.5%, were obtained at a reaction temperature of 110.degree. C. under a reaction pressure of 100 atm for a reaction time of 6 hours (Sci. Cin. Ser. B(Engl. Ed.), 31(3), 269 (1988)). As mentioned above, a very few examples have been made wherein a hydroformylation reaction is carried out by using a phosphonite compound, and fewer examples have been made wherein a phosphonite compound which is not monodentate is used. Further, no example has been known, which reports that a homogeneous complex catalyst containing a bidentate phosphonite compound is effective for the hydroformylation reaction of an olefinic compound.
Further, the activity of the hydroformylation reaction employing a known phosphorus ligand such as a monodentate or bidentate phosphine or a monodentate or bidentate phosphite, has not necessarily been satisfied, and the formation of by-products has brought about an economical disadvantage to commercial production. Among such by-products, paraffins formed by reduction of an olefinic compound by hydrogen gas without a hydroformylation reaction, are particularly valueless. Accordingly, it has strongly been desired to develop a ligand which does not cause a side-reaction such as the hydrogenation reaction.